1. Field of the Invention
The present invention generally relates to pulsed plasma enhanced chemical vapor deposition (PPECVD) and plasma enhanced atomic layer deposition (PEALD) for depositing conformality-tailored films.
2. Description of the Related Art
PPECVD/PEALD processes can provide high conformality (also referred to as “coverage”) of films depositing on a patterned surface on which multiple recesses or grooves are formed in patterns for establishing interconnects, as compared with plasma enhanced chemical vapor deposition (PECVD) processes. However, PEALD processes are typically not as good as thermal ALD in terms of conformality, although PEALD processes are typically better than thermal ALD in terms of deposition rates and controllability, depending on the type of films.
High conformality refers to a high ratio of a thickness of film deposited on a side wall of a recess to a thickness of film deposited on a top surface of the recess. The conformality changes largely depending on the aspect ratio or width of a recess, even if the same processes are used. Recently, since it has been required for semiconductor devices to have more compact and fine structures, when the aspect ratio is 2 to 10 or the width of a recess is 100 nm to 15 nm, in conventional PEALD, the conformality of films may be typically in the range of 50% to 60%, i.e., the thickness of film on the top is approximately twice the thickness of film on the side.
A typical conventional sequence of deposition gas flow and RF power discharge is shown in FIG. 1. In FIG. 1, a deposition gas is introduced in pulses, and a time period between the beginning of a pulse of the deposition gas flow and the beginning of a next pulse of the deposition gas flow constitutes one cycle. RF power is applied also in pulses after the pulse of the deposition gas flow but before the next pulse of the deposition gas flow, so that deposition gas adsorbed on the surface of a substrate is fixed on the surface by plasma. Although not shown in this figure, a reactant gas and a rare gas flow continuously without interruption, and a period between the pulses of the deposition gas is considered to be a purge step. FIG. 2 shows another typical conventional sequence of deposition gas flow and RF power discharge. In this figure, RF power is applied continuously without interruption, while introducing the deposition gas in pulses. By applying RF power continuously, a film such as a Si—N bond-containing film, which has poor adhesion to the substrate surface, can deposit and accumulate on the substrate surface. Also omitted in this figure, reactant gas flow and rare gas flow are continuously conducted.
Normally, the cycle is repeated several tens of times to several hundred times to form a target layer on a patterned surface. As described above, in PEALD for high aspect ratios and/or narrow recesses, the conformality of the resultant film is conventionally typically in the rage of 50% to 60%.
Any discussion of the background art which has been included in the present disclosure is solely for the purpose of providing a context for the present invention, and it should not be taken as an admission that any or all of the discussion form part of the prior art or were known in the art at the time the invention was made.